> The major side effects of NSAIDs are related to their effects on the stomach and bowels (gastrointestinal system). Some 10% to 50% of patients are unable to tolerate treatment with NSAIDs because of side effects, including abdominal pain, diarrhea, and upset stomach. Approximately 15% of patients on long-term treatment with NSAIDs develop a peptic ulcer (ulceration of the stomach or duodenum). Even though many of these patients with ulcers do not have symptoms and are unaware of their ulcers, they are at risk of developing serious ulcer complications, such as bleeding or perforation of the stomach.

This is for a lay audience, but it's not remotely controversial: https://www.medicinenet.com/nonsteroidal_anti-inflammatory_d...